1. Field of the Invention
The present invention relates to automatic transmissions, and more particularly to a hydraulic control system for an automatic transmission of multiple clutch type.
2. Description of the Prior Art
There has heretofore been known an automatic transmission of multiple clutch type having two power transmission shafts each of which transmits power from a driving source such as engine to driving wheels, and having shaft clutches each of which connects or disconnects the corresponding power transmission shaft on a power transmission path (refer to, for example, the official gazette of Japanese Patent Application Publication No. 31031/1988).
The multiple clutch type automatic transmission mentioned above is furnished on the power transmission shafts with a gear shift mechanism which comprises a plurality of speed change gear and dog clutches. The dog clutches select any one of the plurality of speed change gears and render the selected gears capable of transmitting the power. In general, the dog clutches and the aforementioned shaft clutches are selectively engaged by actuating hydraulic cylinders. As a result, any one of the speed change gears mounted on either power transmission shaft is selected to form a specific speed stage.
In the prior-art automatic transmission of the multiple clutch type, however, the fails of the hydraulic cylinders and those of the dog clutches themselves are not especially considered. Accordingly, in a case where the dog clutches have been erroneously engaged by the fails, it is apprehended that the power will circulate due to double engagement, or that the forward range of a motor vehicle will be kept in spite of the reverse range thereof, or vice versa.